5th gear is generally an overdrive gear at aprox 1:1.1 or upto 1:1.2 ratio and not as strong as 4th gear which is usually 1:1 ratio. however having said that I do use 5th gear when only when fairly flat roads so as not to make the vehicle work to hard. I think the trick is to not get the motor into a situation where you put great any strain on the transmission. I usually down shift to 4th gear at the slightest hill and to date have not had any problems. Incidently my manual tow vehicle is a 3.2l 6 cylinder EFI Falcon sedan. Now I only use the falcon about 50% of the time when towing my caravan as it looks much better hooked up behind my 1947 shev pickup which is an auto. ( 1952 plywood caravan )

woo hoooo! 1947 Chevy Pick up sounds great, our tow vehicle is a Holden Rodeo 1999 model, our van is 1980 Viscount. We drive ours in mainly 4th unless there's a good flat road, then will go into 5th. I am starting to help out with the driving and am getting in some practice, haven't got to the backing yet. Fun and games!!! Thanks for your reply, got any pics of the Chevy and van?